This invention relates to ink jet recording or printing method and apparatus. More specifically, the invention is directed toward novel method and apparatus for collecting unused drops in ink jet recording systems of the type wherein a continuous stream of drops are generated and selected drops are directed toward a target and others toward a collection or gutter device.
The continuous drop ink jet system reported by Richard Sweet in U.S. Pat. No. 3,596,275 includes a drop generator that creates a stream of discrete ink drops at a high rate, for example, 100,000 drops per second. The stream passes through a charging tunnel during which time individual drops are assigned a net charge of zero or some finite positive or negative value. Thereafter, the stream of drops flies between a pair of deflection plates having a steady state electric field established between them. The drops are deflected in the direction of the field proportionally to the charge on the drops. A drop collector or gutter is conventionally located between the deflection plates and a target to catch drops not intended for the target. The drops caught by the gutter are circulated back to the drop generator. When text information is being recorded, the number of gutter drops greatly exceeds the number of drops reaching the target. When pictorial information is being recorded, the number of gutter drops can go as low as two percent of the total number.
The gutter is clearly an important element of an ink jet system. But, the presence of a gutter creates packaging and system performance problems especially when the drop generator produces multiple, drop streams each flying between an associated pair of deflection plates. A separate gutter is required for at least every pair of drop streams in this architecture thereby tending to clutter the space between the ends of the deflection plates and the target and otherwise adding to the manufacturing problems and expenses of a recording system. Also, the distance between the ends of the deflection plates and the target should be minimized to enhance the printing operation. The less that distance, the less aerodynamic effects acting on the drops and charge interaction between drops cause drop placement errors on the target.
Accordingly, it is an object here to offset the above noted limitations associated with prior gutter devices employed in fluid drop printing systems using drops from multiple drop streams collectively to compose a record or print on a target. The terms "record" and "print", as well as variations hereof, are used interchangeably herein with no distinction between the two terms being intended.
Still another object of the invention is to remove the gutter devices from the space between the ends of the deflection electrode means and the target thereby enabling a reduction in that space.
Another object of this invention is to incorporate a gutter device into at least those deflection electrode means that are common or shared by adjacent fluid drop streams.
Finally, it is an object of the present invention to devise an improved fluid drop recording system having a compact and efficient architecture for multiple fluid drop stream systems wherein each stream is deflected to greater than two flight paths.
These and other objects of the invention are achieved by the present fluid drop recording method and apparatus. A drop generator produces a plurality of drop streams directed toward a target such as plain paper. The drop streams follow generally parallel flight paths to the target where drops from the plural streams collectively make up a record or print. Each stream passes through a charging electrode where selected drops are charged to desired values. Thereafter, the charged drops are deflected by an electric field in their path established by a pair of deflection electrode means. The drops are charged to different values or levels such that each drop stream is able to place a drop on a predetermined number of pixels or print elements within a segment of an ideal row of such elements. The segments addressed by each neighboring stream begin with the next element within the row. Collectively, the plural streams are able to address every print element within a row across the record. The record and drop generator move relative to each other to compose a two dimensional record or print. This defines a conventional rectangular raster pattern but other geometric raster patterns are possible.
Not all pixel locations receive a drop in normal recording operations, obviously. The drops for those pixels are collected by a gutter which in this invention is located inside a deflection plate means having an orifice facing downstream rather than upstream. In other words, the gutter orifice cannot be intercepted by a drop in flight.
In this invention, fluid in the drops are collected in the gutter means after the drop impacts a collision surface near a curved end surface of the deflection means. The surface tension of the fluid is such that the fluid of an impacting drop flows over the collision surface and around the curved end surface. Thereafter, it flows through an orifice into the gutter.
At least every other deflection electrode means includes a collision surface and a curved end surface on left and right sides next to adjacent left and right drop streams. The gutter means is between the two collision surface and both the curved end surface curve toward each other and therefore the common gutter. One clear advantage in addition to compactness, is that the arrangement of one gutter for every two drop streams is maintained.